JP2000310879A - Color electrophotographic developer - Google Patents

Abstract

(57) [Problem] In particular, there is no problem relating to transferability even in repeated use of a full-color two-component developer, and specifically, there is no deterioration in transfer efficiency, lower image density, poor uniformity, and edge. Provided is a color electrophotographic developer free from defects on an image such as emphasis, image omission, and image color stain. A color electrophotographic developer comprising a carrier having a resin coating layer containing a conductive substance on a core material and toner particles to which an external additive is added, wherein the external additive is silane. A color electrophotographic developer comprising hydrophobic titanium oxide fine particles treated with a coupling agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for color electrophotography used in a copying machine or a laser printer using an electrophotography system.

[0002]

2. Description of the Related Art In recent years, demand for full-color image output in electrophotographic copying machines, printers and the like has been rapidly expanding. Electrophotographic full-color copying generally reproduces all colors by superposing a plurality of layers using four color developers of three primary colors, cyan, magenta, yellow and black. When a two-component developer composed of a toner and a carrier is used as the color developer, each color toner and the carrier are mixed to form a developer. The color toner is a fine powder obtained by mixing, melting, kneading, pulverizing and classifying a binder resin, a coloring agent, a charge controlling agent, and the like, and an external additive such as silica is added to the surface of the toner particles. As a carrier, magnetic metal powder,
Oxide particles and the like are used. Further, in order to reproduce a clear color of an image, each color toner of cyan, magenta, and yellow needs to have a clear color tone. Therefore, as a coloring agent, instead of carbon black used in a normal black and white toner, Various chromatic pigments and dyes are used.

In an image in full-color copying, an original having a high printing rate is often copied, so that uniformity of a solid portion is also important in addition to reproduction of lines and character portions of the image.
Therefore, image quality (such as image density) is higher than that of a normal black and white image.
Is required to be hardly changed with time. However, in general, color developers have difficulty in transferability, and when transfer efficiency is poor, it is difficult to maintain a uniform solid portion over time. Such problems relating to the transferability in the transfer process appear as phenomena such as image density, uniformity deterioration, and edge enhancement of image quality due to deterioration of the transferability of the solid portion due to repeated use of the color developer. In addition, it has been pointed out that toner slightly remains on the photoreceptor, that is, a so-called photoreceptor fogging phenomenon occurs, thereby increasing the load of a cleaning step and reducing transfer efficiency. In particular, in the case of a two-component developer, frictional charging is performed by increasing the contact opportunity and strength by direct contact between the carrier and the color toner. Therefore, when repeatedly used, the above-described problem of deterioration in transferability is likely to become apparent. .

There are many demands for improvement in terms of the transfer process of full-color copying. In the case of using the intermediate transfer material in the transfer of the copying process, the transfer is performed twice, that is, the transfer of the toner image from the photoconductor to the intermediate transfer material and the transfer of the toner image from the intermediate transfer material to the paper. If the transferability of the agent is inferior, the above-mentioned problem is likely to become apparent. In the case where the toner image is directly transferred from the photoconductor to the paper without using the intermediate transfer material, the transfer process is performed once. However, even in this case, transfer to paper is often performed via a conductive transfer material that also serves as paper conveyance, and therefore, the problem of improving the transferability of the developer remains.

Some attempts have been made to solve such problems in repeated use of a full-color two-component developer by improving a so-called external additive of a toner. For example, JP-A-4-333739 discloses a toner composition using a metal oxide fine powder surface-treated with a specific hydrophobizing agent. JP-A-59-52255, JP-A-63-174068, and JP-A-5-188633 disclose toners containing a specific fine powder of titanium oxide. However, these have not always been satisfactory.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color electrophotographic developer which solves the above-mentioned problem of transferability. That is, an object of the present invention is to provide a color free from image defects such as a decrease in image density, poor uniformity, edge emphasis, and image color stains, especially when a full-color two-component developer is used repeatedly without deterioration in transfer efficiency. An object of the present invention is to provide an electrophotographic developer.

[0007]

The gist of the present invention consists of a carrier having a resin coating layer containing a conductive substance on a core material made of metal or metal oxide, and toner particles to which an external additive is added. A color electrophotographic developer, wherein the external additive is hydrophobic titanium oxide fine particles treated with a silane coupling agent.

According to the present invention, as a color developer, titanium oxide fine particles which have been subjected to a hydrophobic treatment with a resin-coated carrier in which a conductive substance represented by carbon black is dispersed and a silane coupling agent represented by alkyltrialkoxysilane. Have been found to have no adverse effects due to the synergistic effect of the combined use with the externally added toner, and have been found to be excellent and effective in improving the transferability, and have reached technical perfection.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, a carrier having a resin coating layer containing a conductive substance is used. As the core material of the carrier, known materials such as magnetic materials such as ferrite powder, magnetite powder, and iron powder having a volume average diameter of 20 to 200 μm are suitably used. Ferrite powder is particularly desirable, and is obtained by firing a metal oxide such as copper, zinc, nickel, manganese, cobalt, and magnesium. Examples of the resin forming the resin coating layer include a silicone resin, a fluorine resin, an acrylic resin, and a styrene resin.In the present invention, the silicone resin is used in view of the sharpness of the obtained charge amount distribution. preferable. As the silicone resin, a so-called straight silicone resin is preferable, and among them, a dimethyl silicone resin is preferable. The coating thickness is 0.1
〜3 μm is preferred. As a coating method, after dissolving or dispersing the resin in an appropriate solvent, any method such as a flow coater method and a dipping method can be used.

As the conductive substance contained in the coating resin layer, various known materials that can be dispersed in the resin layer can be used. For example, carbon black; metal oxides such as tin oxide and magnetite; metal powders such as copper and nickel; Among them, carbon black which can be finely dispersed and can sharpen the distribution of the charge amount is preferable. The amount of the conductive substance is 1 to 20 per 100 parts by weight of the coating resin.
A weight part is preferable and 2 to 10 weight parts is more preferable. If the amount of the conductive substance is less than the above range, the charge amount cannot be sharpened. On the other hand, when the amount is too large, the resin cannot be uniformly dispersed in the resin layer, and the resin layer is easily detached from the coating layer, which may cause a problem of color contamination.

The toner of the present invention has a constitution in which a resin, a colorant, a charge controlling agent and the like are main components and hydrophobic titanium oxide fine particles treated with an alkyl trialkoxysilane are added as an external additive. As the resin constituting the toner, known resins such as polyester resin, styrene resin, and epoxy resin can be used, but in consideration of transparency, fixing property, thermal mechanical strength, and the like required as full color, Desirably, it is a polyester resin. The polyester resin of the present invention comprises a polyhydric alcohol and a polybasic acid, and if necessary, at least one of the polyhydric alcohol and the polybasic acid contains a trifunctional or higher polyfunctional component (crosslinking component). Obtained by polymerizing the composition.

The dihydric alcohol used in the synthesis of the polyester resin includes, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2
Diols such as propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, bisphenol A, Examples thereof include bisphenol A such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylene bisphenol A, and alkylene oxide adducts thereof, and the like. Among these monomers, it is particularly preferable to use a bisphenol A alkylene oxide adduct as a main component monomer, and more preferably an adduct having an average alkylene oxide addition number of 2 to 7 per molecule.

Examples of the trihydric or higher polyhydric alcohol involved in the crosslinking of polyester include sorbitol and 1,1
2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol,
Tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-
Examples thereof include 1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, and others.

On the other hand, polybasic acids include, for example, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid Acids, malonic acid, anhydrides of these acids,
Examples thereof include lower alkyl esters, alkenylsuccinic acids or alkylsuccinic acids such as n-dodecenylsuccinic acid and n-dodecylsuccinic acid, and other divalent organic acids. Among them, it is preferable to use at least terephthalic acid from the viewpoint of thermal stability.

Examples of tribasic or higher polybasic acids involved in the crosslinking of polyester include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid,
1,2,4-cyclohexanetricarboxylic acid, 2,5
7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxy)
Methane, 1,2,7,8-octanetetracarboxylic acid,
And their anhydrides and others.
These polyester resins can be synthesized by a usual method. Specifically, the reaction temperature (170 to 250
C.), reaction pressure (5 mmHg to normal pressure) and the like are determined according to the reactivity of the monomer, and the reaction may be terminated when predetermined physical properties are obtained.

As the colorant, conventionally, cyan, magenta,
Various pigments used for color toners such as yellow,
Dyes can be used. For example, for cyan, a copper phthalocyanine pigment such as Pigment Blue 15 can be used. Examples of magenta pigments include quinacridone pigments such as Pigment Red 122 and azo pigments such as Pigment Red 57: 1. For yellow, azo pigments such as Pigment Yellow 17 and Pigment Yellow 74 are exemplified. Further, these colorants may be subjected to a pre-dispersion treatment (master batch) with a resin for improving dispersion. The amount of the coloring agent used is preferably 1 to 15 parts by weight, and more preferably 2 to 10 parts by weight, based on 100 parts by weight of the resin, although it depends on the required color.

Since the developer of the present invention is preferably used as a load electrode, the charge control agent for the toner is a negative charge control agent for obtaining the load electrode, for example, Japanese Patent Publication No. 3-37183. And metal-containing azo dyes described in JP-B-2-16916 and JP-B-55-4275.
No. 2 and the like, a salicylic acid metal complex,
Salicylic acid metal salts described in 163374 and the like,
Examples thereof include a calixarene compound containing no metal element described in JP-A-5-119535. As a method of including the above-mentioned charge control agent in the toner,
There are a method of adding the toner inside the toner and a method of adding the toner externally. In the case of internal addition, the use amount of these compounds is usually preferably 0.05 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin. When externally added, the amount is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the resin.

In addition, as the auxiliary agent which can be added to the toner for the purpose of improving the thermal characteristics and the physical characteristics, known ones can be used. Examples include alkylene wax, paraffin wax, higher fatty acid, fatty acid amide and the like. The amount of addition is 0.1 to 100 parts by weight of the binder resin.
1 to 10 parts by weight is preferred.

An outline of a method for producing toner particles by a pulverization method is described below. First, a binder resin, a colorant, a charge control agent, and the like, which are constituent materials of the toner, are blended and mixed at a predetermined ratio. As a device at this time, a gravity drop mixer such as a V blender or a ball mill, or a high-speed fluid mixer such as a Henschel mixer (manufactured by Mitsui Miike Kakoki) or a super mixer (manufactured by Kawata) is used. After mixing, the mixture is melt-kneaded. Examples of the apparatus used in the melt-kneading step include a two- or three-roll mill, a Banbury mixer, a single-screw or twin-screw extruder, and the like. In this step, a component having compatibility with the binder resin is melted with the resin, and a component such as a charge control agent having no compatibility with the binder resin is dispersed in the molten resin.

Next, after cooling and solidifying the melt-kneaded material,
The toner particles are manufactured through the steps of coarse pulverization, fine pulverization and classification. Hammer mills and cutter mills are used for coarse pulverization, and mechanical pulverizers such as high-speed rotary pulverizers and jet pulverizers such as impact-type jet mills and fluidized-bed jet mills are used for fine pulverization. For example, a forced vortex type centrifugal classifier or an inertial classifier is used. The toner particles relating to the developer of the present invention have a 50% volume diameter of 5 to 5 after pulverization and classification.
A thickness of 12 μm is preferable because a high-quality image can be obtained. If the thickness is less than 5 μm, the toner scatters violently and fog of an obtained image is deteriorated.
If it exceeds μm, the sharpness of the obtained image tends to decrease, which is not preferable. Measurement of particle size
Laser diffraction particle size distribution measurement system Heros & Ro
Dos (manufactured by SYMPATEC, Germany) is preferably performed under the following conditions, but alternatively, a multisizer (manufactured by Coulter, USA) may be used.

[0021]

[Table 1] Dispersion method: Flow type dispersion unit Dispersion air pressure: 2 bar Lens focal length: 100 mm Measurement time: 3 seconds

In the present invention, these toner particles are
Hydrophobic titanium oxide fine particles treated with a silane coupling agent are externally added. In the present invention, the surface of the titanium oxide fine particles is subjected to a hydrophobic treatment by the above-mentioned silane coupling agent. The silane coupling agent used in the present invention, alkyltrialkoxysilane preferably Among them _{C n H 2n + 1 Si (} OCmH 2m + 1) 3 ( where, n is 3
An integer of 10 and m represents an integer of 1 to 3) are preferred. Specifically, for example, n-butyltrimethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, hexyltrimethoxy Examples thereof include silane, octyltrimethoxysilane, and decyltrimethoxysilane, all of which can be suitably used, and among them, isobutyltrimethoxysilane is more preferable.

The average particle size of the titanium oxide fine particles is 0.3 μm
The thickness is preferably as follows, and more preferably 0.05 to 0.2 μm. It is not preferable that the particle diameter is excessively small from the viewpoint of falling off and burying. The crystal type of the titanium oxide fine particles is preferably a rutile type because the electrical resistance is high and the influence of moisture resistance can be reduced.

As a method of hydrophobizing, while dispersing the titanium oxide fine particles in a solvent, the silane coupling agent of the general formula (1) is dropped and stirred to react, and filtered to obtain hydrophobic titanium oxide fine particles. Is good. The treatment amount of the alkylalkoxysilane is preferably 1 to 30 parts by weight, and more preferably 3 to 20 parts by weight, based on 100 parts by weight of the titanium oxide fine particles. If the treatment amount is smaller than the above, there is a problem in terms of moisture resistance since the hydrophobicity of titanium oxide does not progress. In addition, when the treatment amount is excessive, the agglomeration of the titanium oxide particles becomes severe, so that there is a problem that the fluidity deteriorates. The degree of hydrophobicity can be determined by measuring the degree of hydrophobicity of methanol, and the hydrophobicity of the hydrophobic titanium oxide fine particles in the present invention is preferably 45% or more, more preferably 50 to 80%. % Is good.
To measure the hydrophobicity of methanol, 50 ml of distilled water is placed in a beaker, and then 0.2 g of external additive fine particles are gently added. The tip of the burette filled with methanol is immersed in water so as not to touch the fine particles of the external additive. Record the amount of methanol dropped until it settles in water. The methanol hydrophobicity is calculated from the following equation.

[0025]

W = Vm / (50 + Vm) × 100 W: Degree of hydrophobicity of methanol (%) Vm: Dropping amount of methanol (ml)

The toner may be added in the amount of toner particles 1
0.05 parts by weight of hydrophobic titanium oxide fine particles
It is preferable to add about 1 part by weight by external addition. When the addition amount is small, the effect of suppressing the high charge amount portion of the toner is too small to improve the transferability. Excessive addition is not preferable because it tends to cause image defects due to thickening of lines and character portions. The toner according to the present invention may contain other known external additives in addition to the hydrophobic titanium oxide fine particles. For example, fine particles of inorganic oxides such as silica and alumina, which may be subjected to a hydrophobic treatment, and resin beads such as polymethyl methacrylate, Teflon, and silicone resin are exemplified.

The transferability problems of the color electrophotographic developer of the present invention, such as excellent transferability of a solid portion even in repeated use, are greatly improved, and it is not always clear why it can be suitably used for full-color copying. But,
It is considered as follows. That is, by incorporating carbon black into the resin coating layer as a conductive substance, the ability to impart charge to the toner as a carrier is weakened and the charge as a developer can be reduced, so that reproduction of the image solid portion can be easily achieved. . However, repeated use causes a problem of color contamination due to desorption of carbon black which is fatal for photoreceptor fogging and color use. If the amount of carbon black is reduced to a range where there is no color contamination for the improvement, the solid reproduction performance tends to be slightly deteriorated.

When such a carrier is used in combination with a toner to which specific hydrophobic titanium oxide fine particles according to the present invention are externally added, the external additive is less likely to fall off and be embedded even in repeated use. Can improve the image solid at the time of repeated use, which was insufficient. Also,
Since the toner image on the photoconductor can be made non-adhesive, transfer from the photoconductor becomes easy. In order to obtain the same performance by using these external additives alone, it is necessary to increase the amount of excessive addition, and a thickening phenomenon of lines and characters occurs. However, when used in combination with a carrier having a carbon black dispersion coating layer capable of lowering the charge as a developer, the addition amount of the toner external additive is small, so that line thickening does not occur. The present invention has a technical feature in that various problems of transferability, which cannot be solved by the carrier and the toner alone, are solved by a combined interaction.

[0029]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples. In Examples and Comparative Examples, "parts" indicates "parts by weight". Example A magenta toner, a cyan toner, a yellow toner, and a black toner were prepared with the compositions described below.

[0030]

[Table 2] Magenta toner Resin: polyester resin A (* 1) 92.5 parts Coloring agent: CI Pigment Red 57: 1 masterbatch pigment (* 2) 12.5 parts Charge control agent: Bontron E-81 (manufactured by Orient Chemical Co., Ltd.) 2 parts Wax: Viscole 660P (manufactured by Sanyo Chemical) 2 parts

(* 1) A resin polymerized from a polypropylene oxide adduct of bisphenol A and terephthalic acid was used. The molecular weight peak of the resin by gel permeation chromatography is about 8,000. (* 2) CIPigment Red 57: 1 and 40 of polyester resin A
Parts: 60 parts were kneaded with a two-roll mill for 30 minutes to obtain a master batch pigment.

[0032]

[Table 3] Cyan toner Resin: Polyester resin A (* 1) 92.5 parts Colorant: CI Pigment Blue 15: 3 type master batch pigment (* 3) 12.5 parts Charge control agent: Bontron E-81 (manufactured by Orient Chemical Co., Ltd.) 2 Wax: Viscole 660P (manufactured by Sanyo Chemical) 2 parts

(* 1) Same resin as magenta toner. (* 3) 4 of CI Pigment Blue 15: 3 and polyester resin A
0 parts: 60 parts were kneaded with a two-roll mill for 30 minutes to obtain a master batch pigment.

[0034]

[Table 4] Yellow toner Resin: 92.5 parts of polyester resin A (* 1) Colorant: 12.5 parts of CI Pigment Yellow 17 type masterbatch pigment (* 4) Charge control agent: Bontron E-81 (manufactured by Orient Chemical Co.) 2 parts Wax : Viscole 660P (manufactured by Sanyo Chemical) 2 copies

(* 1) Same as magenta toner. (* 2) CIPigment Yellow 17 and polyester resin A 40
Parts: 60 parts were kneaded with a two-roll mill for 30 minutes to obtain a master batch pigment.

[0036]

[Table 5] Black toner Resin: Polyester resin A (* 1) 100 parts Colorant: Mitsubishi Carbon Black MA100 (Mitsubishi Chemical) 5 parts Charge control agent: Bontron E-81 (Orient Chemical) 2 parts Wax: Viscole 660P (manufactured by Sanyo Chemical) 2 copies (* 1) Same as magenta toner.

The toner is manufactured by mixing the raw materials for each color with a high-speed fluid mixer, melt-kneading with a twin-screw extruder, coarsely pulverizing with a hammer mill, and using a mechanical pulverizer Kryptron (manufactured by Kawasaki Heavy Industries, Ltd.). ) And then classified with a zigzag classifier (Alpine). On the other hand, hydrophobic titanium oxide fine particles obtained by subjecting 100 parts of rutile type titanium dioxide fine particles having an average primary particle diameter of about 0.05 μm to hydrophobic treatment using 10 parts of an isobutyltrimethoxysilane coupling agent as an external additive. 1 was prepared. For external addition to each toner, 0.5 part of hydrophobic titanium oxide fine particles 1 and 0.5 part of hydrophobic silica H2000 (manufactured by Wacker Inc.) were added to 100 parts of each toner using a Henschel mixer (manufactured by Mitsui Miike Co., Ltd.). ).

The volume average particle diameter of each color toner is 8.5 to 9.0.
μm. As a carrier, Cu-Zn ferrite with a volume average particle diameter of about 60 μm is used as a core material, and carbon black (Mitsubishi Carbon Black # 44, Mitsubishi Chemical Corporation) is used as a coating agent for 100 parts of a resin solid content of a toluene solution of dimethyl silicone resin. 10 parts) and dispersed with a homogenizer. The coated carrier is prepared by charging a core into a flow coater, blowing hot air from the lower part of the coater to flow, spraying the coating liquid from a nozzle inside the coater to adsorb the resin liquid to the core, and performing a sufficient heat treatment. Was prepared. The thickness of the carrier coating layer was about 1 μm as observed by a scanning electron microscope.

5 parts of each toner and 95 parts of the carrier are
The mixture was mixed by a mold mixer to obtain a developer of each color. Using the toner and developer of each color described above, evaluation was made by actual photography. As the actual image evaluation apparatus, an apparatus obtained by modifying a commercially available two-component developing type full-color copying machine was used. The developing unit of this apparatus includes magenta, cyan, yellow, and black developing machines, and the transfer unit includes an intermediate transfer belt. The evaluation is carried out by setting the copying machine in a normal temperature and normal humidity atmosphere at a temperature of 25 ° C. and a relative humidity of 55%, charging the developers of the respective colors into the respective developing machines, and replenishing the toner by continuous actual photographing.

Table 1 shows the evaluation results. The evaluation result was excellent. The image quality such as image density, uniformity, and edge enhancement hardly fluctuated over 20000 actual images, and the fog of the photoconductor (OPC) was very small, and the transfer efficiency was 90%.
% Was excellent. In addition, there was no scattering of the toner into the apparatus during the actual photographing, no poor cleaning on the photoreceptor and no occurrence of the toner fusing phenomenon were observed, and the toner had sufficient durability.

[0041]

[Table 6]

Evaluation method Developer charge: Suction blow-off TB- manufactured by Toshiba Chemical Corporation
Measured by Model 201 Toner concentration: Separates toner from developer with aqueous surfactant solution and measures by gravimetric method Transfer efficiency: Measures the weight of toner recovered by cleaning and the weight of replenished toner, and the ratio (Percentage) Image density: Measure the image density with a Gretag colorimeter SPM-50. Photoreceptor fog: Adhere a transparent adhesive tape to the surface of the photoreceptor after development with a blank original, peel off, and then peel off the Macbeth image densitometer RD914. Measure the image density with the following: Image missing, edge enhancement, solid uniformity, image stain:
Observe the obtained image with a loupe and judge according to the following criteria. ：: Poor solid uniformity, missing image, edge enhancement, no image color stain observed △: Poor solid uniformity, missing image, edge enhanced , Image color stain is slightly observed, but there is no problem in practical use. ×: Poor solid uniformity, omission in image, edge emphasis, image color stain are clearly seen, and there is a practical problem.

On the other hand, the developer and the printer were heated to a temperature of 35.
℃, relative humidity of 85% high-temperature and high-humidity conditions, the same continuous actual shooting was performed, but the charge amount was slightly lower than in the case of normal temperature and normal humidity environment conditions, but there was no practical problem Obtained. Further, the developer and the printer are set at a temperature of 10
The same continuous shooting was performed under high temperature and high humidity conditions of 20 ° C. and a relative humidity of 20%, but the result was almost the same as the result in a normal temperature and normal humidity environment.

Comparative Example 1 (Carbon black in resin coating layer)
In the examples, a developer was used in exactly the same manner as in the examples except that a dimethyl silicone resin solution not dispersing carbon black alone was used to form a resin coating layer of about 1 μm as a coating agent for the carriers used. Was prepared, and an actual photograph was evaluated. Table 2 shows the evaluation results. Image quality fluctuations such as a decrease in image density and a decrease in uniformity are observed in repeated actual photographing, which poses a practical problem.

[0045]

[Table 7]

Comparative Example 2 (External addition of hydrophobic titanium oxide fine particles
Using toner not used) In the examples, toner of each color was prepared by externally adding only hydrophobic silica without adding hydrophobic titanium oxide fine particles as an external additive of the toner to be used . Hereinafter, a developer was prepared exactly in the same manner as in the example, and an actual image was evaluated. Table 2 shows the evaluation results. In repeated actual shootings, transfer efficiency, photoreceptor fog, and the like are deteriorated, which poses a practical problem.

[0047]

[Table 8]

[0048]

According to the present invention, there are no problems relating to transferability even in the repeated use of a full-color two-component developer, specifically, there is no deterioration in transfer efficiency, a decrease in image density, poor uniformity, and an edge. A color electrophotographic developer free from defects on the image such as enhancement, omission in the image, and stain on the image color can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hirotaka Tashiro 1 Fukudacho, Joetsu City, Niigata Prefecture Inside the Naoetsu Works, Mitsubishi Chemical Corporation (72) Inventor Toshihiko 1 Fukudacho, Joetsu City, Niigata Prefecture Naoetsu Business, Mitsubishi Chemical Corporation Office (72) Inventor Yoshihiro Kigami 1 Fukudacho, Joetsu City, Niigata Prefecture Inside the Naoetsu Plant, Mitsubishi Chemical Corporation (72) Inventor Yukihiro Sato 1 Fukudacho, Joetsu City, Niigata Prefecture F Term in the Naoetsu Office, Mitsubishi Chemical Corporation (Reference) 2H005 AA08 AA21 BA02 BA06 BA07 CA12 CA21 CA26 CB07 CB18 DA09 EA07 FA01 FC01

Claims (8)

[Claims] 1. A color electrophotographic developer comprising a carrier having a resin coating layer containing a conductive substance on a core material and toner particles to which an external additive has been added, wherein the external additive comprises: A developer for color electrophotography, comprising hydrophobic titanium oxide fine particles treated with a silane coupling agent. 2. The method according to claim 1, wherein the silane coupling agent is C _n H
_{2n + 1 Si (OCmH 2m +1} ) 3 ( where, n is 3 to 10 integer, m is an integer of 1 to 3) developing electrophotographic color according to claim 1 is represented by Agent. 3. The color electrophotographic developer according to claim 1, wherein the hydrophobic titanium oxide fine particles have a rutile type crystal. 4. The color electrophotographic developer according to claim 1, wherein the silane coupling agent is isobutyltrimethoxysilane. 5. The color electrophotographic development according to claim 1, wherein 0.05 to 1 part by weight of said hydrophobic titanium oxide fine particles is externally added to 100 parts by weight of said toner particles. Agent. 6. The color electrophotographic developer according to claim 1, wherein the resin constituting the resin coating layer is a silicone resin. 7. The color electrophotographic developer according to claim 1, wherein the conductive substance is carbon black. 8. The color electrophotographic development according to claim 1, wherein the conductive material is contained in an amount of 1 to 20 parts by weight based on 100 parts by weight of the resin forming the resin coating layer. Agent.